The present invention relates to a process for the production of tantalum-niobium concentrates from low-tantalum, high-niobium raw materials with an Nb.sub.2 O.sub.5 Ta.sub.2 O.sub.5 ratio of 5 to 15 in a pyrometallurgical concentration process.
Tantalum is generally obtained by wet chemical methods, for example from tantalum concentrates and/or from tin slag arising from smelting tin stone (cassiterite, SnO.sub.2). The concentrate may be economically processed by wet chemical methods only if a ratio of tantalum to niobium of 1:5 is not exceeded and the Ta.sub.2 O.sub.5 content is greater than 10 wt. %.
Tin slag with a low useful material content, the tantalum and niobium oxide content of which is so low that wet chemical processing would be uneconomical, is upgraded by pyrometallurgical processes, for example by reduction with carbon with the addition of slag forming fluxes in an electric-arc furnace to yield synthetic concentrates.
German patent application 27 33 193 thus describes a process for the concentration of tantalum and niobium. The aim of this process is to process high-TiO.sub.2 raw materials, wherein titanium and tin are, as far as possible, separated from tantalum and niobium. The useful materials tantalum and niobium are jointly concentrated in a metallic alloying stage, such that both tantalum and niobium are present in metallic form. Aluminium is used as the reducing agent and barytes as the slag forming flux.
U.S. patent application Ser. No. 2,909,427 discloses a process for the production of ferroniobium by means of purposeful reduction. The aim of the process is to produce a low-tantalum ferroniobium containing neither tin nor phosphorus. To this end, tin and phosphorus are reduced in a first stage in a bath of iron in an electric-arc furnace with a basic lining, while tantalum and niobium remain as oxides in the slag. In a second stage, which is also performed in a furnace vessel with a basic lining and with the addition of slag forming fluxes, the tantalum is separated from the niobium. Niobium is reduced to ferroniobium by using aluminium as the reducing agent, while the tantalum is intended as far as possible to remain in the slag. There is no description of a purposeful concentration of tantalum nor of its isolation.
The object of the invention is specifically to make it possible to concentrate tantalum from a low-tantalum, high-niobium raw material with the aim of ensuring that customary wet chemical opening-up of tantalum-niobium concentrates may subsequently be performed economically. The emphasis thus lies upon the isolation of tantalum from raw materials which are high in niobium but low in tantalum. The process is preferably to be used for columbite ores and/or tin slag with a tantalum-niobium ratio of 1:5 to 1:15.